Combined dolan bridge and quantum dot josephson junction in series

ABSTRACT

A method of producing a quantum circuit includes forming a mask on a substrate to cover a first portion of the substrate, implanting a second portion of the substrate with ions, and removing the mask, thereby providing a nanowire. The method further includes forming a first lead and a second lead, the first lead and the second lead each partially overlapping the nanowire. In operation, a portion of the nanowire between the first and second leads forms a quantum dot, thereby providing a quantum dot Josephson junction. The method further includes forming a third lead and a fourth lead, one of the third and fourth leads partially overlapping the nanowire, wherein the third lead is separated from the fourth lead by a dielectric layer, thereby providing a Dolan bridge Josephson junction. The nanowire is configured to connect the quantum dot Josephson junction and the Dolan bridge Josephson junction in series.

BACKGROUND

The present invention relates to Josephson junctions, and morespecifically, to a Dolan bridge Josephson junction and a quantum dotJosephson junction connected in series.

Quantum computers require large numbers of qubits, and combiningdifferent types qubits in a single quantum processor may beadvantageous. For example, the ability to combine different types ofqubits may have applications in frequency tuning, quantum memory,sensing of qubit states, error correction, and redundancy.

SUMMARY

According to an embodiment of the present invention, a method ofproducing a quantum circuit includes forming a mask on a substrate tocover a first portion of the substrate, implanting a second portion ofthe substrate not covered by the mask with ions, and removing the mask,thereby providing a nanowire comprising the first portion of thesubstrate. The method further includes forming a first lead and a secondlead on top of the substrate, the first lead being spaced apart from thesecond lead, the first lead and the second lead each partiallyoverlapping the nanowire, wherein, in operation, a portion of thenanowire between the first and second leads forms a quantum dot, therebyproviding a quantum dot Josephson junction. The method further includesforming a third lead and a fourth lead on top of the substrate, one ofthe third lead and the fourth lead partially overlapping the nanowire,wherein the third lead is separated from the fourth lead by a dielectriclayer, thereby providing a Dolan bridge Josephson junction. The nanowireis configured to connect the quantum dot Josephson junction and theDolan bridge Josephson junction in series.

According to an embodiment of the present invention, a quantum circuitincludes a substrate, the substrate including a first portion forming ananowire and a second portion surrounding the first portion. The quantumcircuit includes a first lead and a second lead formed on top of thesubstrate, the first lead being spaced apart from the second lead, thefirst lead and the second lead each partially overlapping the nanowire,wherein, in operation, a portion of the nanowire between the first andsecond leads forms a quantum dot, thereby providing a quantum dotJosephson junction. The quantum circuit includes a third lead and afourth lead formed on top of the substrate, one of the third lead andthe fourth lead partially overlapping the nanowire, wherein the thirdlead is separated from the fourth lead by a dielectric layer, therebyproviding a Dolan bridge Josephson junction. The nanowire is configuredto connect the quantum dot Josephson junction and the Dolan bridgeJosephson junction in series. According to an embodiment of the presentinvention, a quantum computer includes a refrigeration system undervacuum comprising a containment vessel, and a qubit chip containedwithin a refrigerated vacuum environment defined by the containmentvessel, wherein the qubit chip includes a quantum circuit. The quantumcomputer includes an electromagnetic waveguide arranged within therefrigerated vacuum environment so as to direct electromagnetic energyto and receive electromagnetic energy from the quantum circuit. Thequantum circuit includes a substrate, the substrate including a firstportion forming a nanowire and a second portion surrounding the firstportion. The quantum circuit includes a first lead and a second leadformed on top of the substrate, the first lead being spaced apart fromthe second lead, the first lead and the second lead each partiallyoverlapping the nanowire, wherein, in operation, a portion of thenanowire between the first and second leads forms a quantum dot, therebyproviding a quantum dot Josephson junction. The quantum circuit includesa third lead and a fourth lead formed on top of the substrate, one ofthe third lead and the fourth lead partially overlapping the nanowire,wherein the third lead is separated from the fourth lead by a dielectriclayer, thereby providing a Dolan bridge Josephson junction. The nanowireis configured to connect the quantum dot Josephson junction and theDolan bridge Josephson junction in series.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a flowchart that illustrates a method of producing a quantumcircuit according to an embodiment of the current invention.

FIG. 2 is a schematic illustration of a quantum circuit according to anembodiment of the present invention.

FIG. 3A is a schematic illustration of a plan view of a substrate.

FIG. 3B is a schematic illustration of a cross-sectional view of asubstrate.

FIG. 4A is a schematic illustration of a plan view of a substrate with ananowire formed therein.

FIG. 4B is a schematic illustration of a cross-sectional view of asubstrate with a nanowire formed therein.

FIG. 5A is a schematic illustration of a plan view of a substrate with aliftoff mask formed thereon.

FIG. 5B is a schematic illustration of a cross-sectional view of asubstrate with a liftoff mask formed thereon.

FIG. 6A is a schematic illustration of a plan view of a substrate with aliftoff mask formed thereon, and a metal deposited on the substrate andliftoff mask.

FIG. 6B is a schematic illustration of a cross-sectional view of asubstrate with a liftoff mask formed thereon, and a metal deposited onthe substrate and liftoff mask.

FIG. 7A is a schematic illustration of a plan view of a substrate with aleads of a quantum dot Josephson junction formed thereon.

FIG. 7B is a schematic illustration of a cross-sectional view of asubstrate with a leads of a quantum dot Josephson junction formedthereon.

FIG. 8A is a schematic illustration of a plan view of a substrate with aliftoff mask having a first layer and a second layer formed thereon.

FIG. 8B is a schematic illustration of a cross-sectional view of asubstrate with a liftoff mask having a first layer and a second layerformed thereon.

FIG. 9A is a schematic illustration of a plan view of a substrate with ametal layer deposited on the second layer of the liftoff mask.

FIG. 9B is a schematic illustration of a cross-sectional view of asubstrate with a metal layer deposited on the second layer of theliftoff mask.

FIG. 10A is a schematic illustration of a plan view of the device ofFIG. 9A after removal of the liftoff mask.

FIG. 10B is a schematic illustration of a cross-sectional view of thedevice of FIG. 9B after removal of the liftoff mask.

FIG. 11 is a schematic illustration of a quantum computer according toan embodiment of the present invention.

DETAILED DESCRIPTION

FIG. 1 is a flowchart that illustrates a method 100 of producing aquantum circuit according to an embodiment of the current invention. Themethod 100 includes forming a mask on a substrate to cover a firstportion of the substrate 102, and implanting a second portion of thesubstrate not covered by the mask with ions 104. The method 100 includesremoving the mask, thereby providing a nanowire comprising the firstportion of the substrate 106. The method 100 includes forming a firstlead and a second lead on top of the substrate, the first lead beingspaced apart from the second lead, the first lead and the second leadeach partially overlapping the nanowire, wherein, in operation, aportion of the nanowire between the first and second leads forms aquantum dot, thereby providing a quantum dot Josephson junction 108. Themethod 100 includes forming a third lead and a fourth lead on top of thesubstrate, one of the third lead and the fourth lead partiallyoverlapping the nanowire, wherein the third lead is separated from thefourth lead by a dielectric layer, thereby providing a Dolan bridgeJosephson junction 110. The nanowire is configured to connect thequantum dot Josephson junction and the Dolan bridge Josephson junctionin series.

According to an embodiment of the present invention, forming the firstlead and the second lead may include forming the first lead and thesecond lead to be substantially perpendicular to the nanowire.

According to an embodiment of the present invention, forming the thirdlead and the fourth lead includes forming the third lead on thesubstrate such that the third lead partially overlaps the nanowire,oxidizing the third lead to form the dielectric layer, and forming thefourth lead in contact with the dielectric layer.

The third lead may extend substantially perpendicular to the fourthlead, and to the nanowire. However, the embodiments of the invention arenot limited to this configuration.

According to an embodiment of the present invention, the method 100further includes forming a nanowire source lead and a nanowire drainlead on the substrate. The nanowire source lead may be formed to overlapthe nanowire at a first end of the nanowire, and the nanowire drain leadmay be formed to overlap the nanowire at a second end of the nanowireopposing the first end.

According to an embodiment of the present invention, at least one of theforming the first and second leads and the forming the third and fourthleads includes lift off processing.

FIG. 2 is a schematic illustration of a quantum circuit 200 according toan embodiment of the present invention. The quantum circuit 200 includesa substrate 202. The substrate 202 includes a first portion forming ananowire 204 and a second portion 206 surrounding the first portion. Thequantum circuit 200 includes a first lead 210 and a second lead 212formed on top of the substrate 202. The first lead 210 is spaced apartfrom the second lead 212, and the first lead 210 and the second lead 212each partially overlap the nanowire 204. In operation, a portion 220 ofthe nanowire 204 between the first lead 210 and the second lead 212forms a quantum dot, thereby providing a quantum dot Josephson junction208. The quantum circuit 200 includes a third lead 216 and a fourth lead218 formed on top of the substrate 202. One of the third lead 216 andthe fourth lead 218 partially overlaps the nanowire 204. The third lead216 is separated from the fourth lead 218 by a dielectric layer, therebyproviding a Dolan bridge Josephson junction 214. The nanowire 204 isconfigured to connect the quantum dot Josephson junction 208 and theDolan bridge Josephson junction 214 in series.

According to an embodiment of the present invention, the first andsecond leads 210, 212 of the quantum dot Josephson junction 208 extendsubstantially perpendicular to the nanowire 204. However, embodiments ofthe invention are not limited to this configuration. The first andsecond leads 210, 212 of the quantum dot Josephson junction 208 may haveother orientations with respect to each other, and to the nanowire 204.

According to an embodiment of the present invention, the first portionof the substrate 202 forming the nanowire 204 includes indium arsenide(InAs), and the second portion 206 of the substrate 202 includes InAsimplanted with ions. The substrate may include other materials besidesor in addition to InAs, for example, 3-5 materials, gallium arsenide(GaAs), or indium gallium arsenide (InGaAs). The ions may be, forexample, hydrogen, oxygen, helium, or argon. The nanowire 204 accordingto an embodiment of the present invention has a width less than 50 nm,and a length between 100 nm and 1000 nm. The nanowire 204 according toan embodiment of the present invention has a length between 500 nm and1000 nm.

According to an embodiment of the present invention, the third lead 216of the Dolan bridge Josephson junction 214 extends substantiallyperpendicular to the fourth lead 218. The third lead 216 of the Dolanbridge Josephson junction 214 may also extend substantiallyperpendicular to the nanowire 204. However, embodiments of the inventionare not limited to these orientations of the third lead 216 with respectto the fourth lead 218 and the nanowire 204.

According to an embodiment of the present invention, the quantum circuit200 includes a nanowire source lead 222 and a nanowire drain lead 224formed on the substrate 202. The nanowire source lead 222 overlaps thenanowire 204 at a first end of the nanowire 204, and the nanowire drainlead 224 overlaps the nanowire 204 at a second end of the nanowire 204.The nanowire source lead 222 and nanowire drain lead 224 can be run outto pads, and can contact the pads directly with wire bonding or othermethods. The pads can be used to control the current through thenanowire to connect the quantum dot Josephson junction 208 and the Dolanbridge Josephson junction 214 in series.

FIGS. 3A-10B are schematic illustrations of a process that can be usedto form a quantum circuit according to an embodiment of the presentinvention. In FIGS. 3A-10B, like reference numerals refer to likefeatures, for example, reference numeral 300 in FIG. 3B and 400 in FIG.4B both refer to a substrate. The process schematically illustrated inFIGS. 3-12 may employ liftoff processing techniques.

FIGS. 3A and 3B are schematic illustrations of a plan view and across-sectional view of a substrate 300. The substrate 300 may include,for example, InAs. The substrate 300 may include a capping layer 302.The process of forming a quantum circuit may include forming a nanowirein the substrate 300. The process of forming the nanowire may includeforming a photoresist 304 to cover a first portion 306 of the substrate300, and then implanting a second portion 308 of substrate 300 notcovered by the mask 304 with ions, and removing the mask 304. Accordingto an embodiment of the present invention, the second portion 308 of thesubstrate 300 is implanted with helium or hydrogen ions. The photoresist304 may have a size that is substantially the size of the nanowire to beformed. The photoresist 304 may be formed, for example, using a 193expose tool and off-axis illumination, such as dipole illumination, orquadrupole illumination. The pattern may be formed in resist and used assuch, or it may be etched into a hard mask, such as Si or Ti, and areactive ion etching process can be used to shrink the size of theresist space, if needed, for example, from 70 nm to 50 nm or smaller.

FIGS. 4A and 4B are schematic illustrations of a plan view and across-sectional view of a substrate 400 with a nanowire 408 formedtherein. The first portion 306 of the substrate 300 in FIG. 3B forms thenanowire 408.

The process of forming a quantum circuit includes forming a quantum dotJosephson junction on the substrate. FIGS. 5A and 5B are schematicillustrations of a plan view and a cross-sectional view of a substrate500 with a liftoff mask 510 formed thereon. The liftoff mask 510 ispatterned for formation of the quantum dot, as well as source and drainleads for the nanowire 508. Patterning the resist 510 may includedepositing the resist, exposing it, and developing it.

FIGS. 6A and 6B are schematic illustrations of a plan view and across-sectional view of a substrate 600 with a liftoff mask 610 formedthereon, and a metal 612 deposited on the substrate 600 and liftoff mask610. The metal 612 may be deposited by evaporation, for example, whichcan be directional enough not to coat the sidewalls of the lift offstack. Alternatively, the metal 612 may be deposited by, for example,molecular-beam epitaxy, sputter deposition, or chemical vapor depositionwith a directional ion control method. The deposition methods describedherein are provided as examples, and the embodiments of the inventionare not limited to these deposition methods. The metal 612 may be anymetal used for quantum dot Josephson junction wiring, as long as it doesnot have sufficient stress to distort the liftoff mask 610. The metal612 may include, for example, aluminum, lead, titanium, tungsten, orvanadium. After deposition of the metal 612, the process includeslifting off the liftoff mask 610.

FIGS. 7A and 7B are schematic illustrations of a plan view and across-sectional view of a substrate 700 with a leads of a quantum dotJosephson junction 714 formed thereon. The quantum dot Josephsonjunction 714 includes a first lead 716 and a second lead 718 spacedapart from the first lead 716. The first lead 716 and the second lead718 each partially overlap the nanowire 708. A portion of the nanowire708 between the first and second leads 716, 718 of the quantum dotJosephson junction 714 forms a quantum dot 720.

The process of forming a quantum circuit may include forming a nanowiresource lead 722 and a nanowire drain lead 724 on the substrate 700. Thenanowire source 722 lead may be formed to overlap the nanowire 708 at afirst end, and the nanowire drain lead 724 may be formed to overlap thenanowire 708 at a second end opposing the first end.

The process of forming a quantum circuit includes forming a Dolan bridgeJosephson junction on top of the substrate. FIGS. 8A and 8B areschematic illustrations of a plan view and a cross-sectional view of asubstrate 800 with a liftoff mask having a first layer 826 and a secondlayer 828 formed thereon. The first layer 826 and the second layer 828are patterned to exposed portions of the substrate 800 on which theDolan bridge Josephson junction will be formed. The first layer 826 mayinclude, for example, an organic polymer. The second layer 828 mayinclude, for example, titanium or silicon. The first layer 826 andsecond layer 828 may be chosen such that etching exposes a portion ofthe substrate 800 that is larger than the area of the opening in thesecond layer 828. For example, the first layer 826 and second layer 828may be etched using reactive ion etching. The etching may etch the firstlayer 826 more quickly than the second layer 828.

FIGS. 9A and 9B are schematic illustrations of a plan view and across-sectional view of a substrate 900 with a metal layer 930 depositedon the second layer 928 of the liftoff mask. The metal layer 930 mayinclude, for example, aluminum, lead, titanium, tungsten, vanadium, orniobium, for example, and the deposition method may be directional. Themetal layer 930 according to an embodiment of the present invention maybe deposited in two steps: 90 degree metal evaporation and 45 degreemetal evaporation. The 90 degree evaporation results in a third lead 932of the Dolan bridge Josephson junction. The 45 degree evaporationresults in a fourth lead 934. The third lead 932 may be exposed tooxygen prior to formation of the fourth lead 934, forming an oxide layerbetween the third lead 932 and the fourth lead 934. The oxide layer actsas the dielectric layer of the Dolan bridge Josephson junction. However,embodiments of the invention are not limited to the dielectric layerbeing an oxide layer. Alternative methods for forming the dielectriclayer may be used. One of the third lead 932 and the fourth lead 934partially overlaps the nanowire. As shown in FIG. 9A, the third lead 932partially overlaps the nanowire.

FIGS. 10A and 10B are schematic illustrations of a plan view and across-sectional view of the device of FIGS. 9A and 9B after removal ofthe liftoff mask. The nanowire 1008 connects the quantum dot Josephsonjunction 1014 and the Dolan bridge Josephson junction 1036 in series.

FIG. 11 is a schematic illustration of a quantum computer 1100 accordingto an embodiment of the present invention. The quantum computer 1100includes a refrigeration system under vacuum including a containmentvessel 1102, and a qubit chip 1104 contained within a refrigeratedvacuum environment defined by the containment vessel 1102. The qubitchip 1104 includes a quantum circuit. The quantum computer 1100 includesan electromagnetic waveguide 1106 arranged within the refrigeratedvacuum environment so as to direct electromagnetic energy to and receiveelectromagnetic energy from the quantum circuit. The quantum circuitincludes a substrate, the substrate including a first portion forming ananowire 1108 and a second portion 1110 surrounding the first portion.

The quantum circuit includes a first lead 1114 and a second lead 1116formed on top of the substrate. The first lead 1114 is spaced apart fromthe second lead 1116. The first lead and the second lead each partiallyoverlap the nanowire 1108. In operation, a portion of the nanowire 1108between the first and second leads 1114, 1116 forms a quantum dot,thereby providing a quantum dot Josephson junction 1112.

The quantum circuit includes a third lead 1120 and a fourth lead 1122formed on top of the substrate. One of the third lead 1120 and thefourth lead 1122 partially overlaps the nanowire 1108. The third lead1120 is separated from the fourth lead 1122 by a dielectric layer,thereby providing a Dolan bridge Josephson junction 1118. The nanowire1108 is configured to connect the quantum dot Josephson junction 1112and the Dolan bridge Josephson junction 1118 in series.

According to an embodiment of the present invention, the first andsecond leads 1114, 1116 of the quantum dot Josephson junction 1112extend substantially perpendicular to the nanowire 1108. However,embodiments of the invention are not limited to this configuration. Thefirst and second leads 1114, 1116 of the quantum dot Josephson junction1112 may have other orientations with respect to each other, and to thenanowire 1108.

According to an embodiment of the present invention, the first portionof the substrate forming the nanowire 1108 includes indium arsenide(InAs), and the second portion of the substrate includes InAs implantedwith ions. The ions may include, for example, helium ions or hydrogenions. The nanowire 1108 according to an embodiment of the presentinvention has a width less than 50 nm, and a length between 100 nm and1000 nm. The nanowire 1108 according to an embodiment of the presentinvention has a length between 500 nm and 1000 nm.

According to an embodiment of the present invention, the third lead 1120of the Dolan bridge Josephson junction 1118 extends substantiallyperpendicular to the fourth lead 1122. The third lead 1120 of the Dolanbridge Josephson junction 1118 may also extend substantiallyperpendicular to the nanowire 1108. However, embodiments of theinvention are not limited to these orientations of the third lead 1120with respect to the fourth lead 1122 and the nanowire 1108.

According to an embodiment of the present invention, the quantum circuit200 includes a nanowire source lead 222 and a nanowire drain lead 224formed on the substrate 202. The nanowire source lead 222 overlaps thenanowire 204 at a first end of the nanowire 204, and the nanowire drainlead 224 overlaps the nanowire 204 at a second end of the nanowire 204.

According to an embodiment of the present invention, method of producinga nanowire includes forming a mask on a substrate to cover a firstportion of the substrate, implanting a second portion of the substratenot covered by the mask with ions, and removing the mask, therebyproviding a nanowire comprising the first portion of the substrate. Anexample of the method of producing a nanowire is schematicallyillustrated in FIGS. 3A-4B. The ions according to an embodiment of thepresent invention may include helium ions or hydrogen ions.

The descriptions of the various embodiments of the present inventionhave been presented for purposes of illustration, but are not intendedto be exhaustive or limited to the embodiments disclosed. Manymodifications and variations will be apparent to those of ordinary skillin the art without departing from the scope and spirit of the describedembodiments. The terminology used herein was chosen to best explain theprinciples of the embodiments, the practical application or technicalimprovement over technologies found in the marketplace, or to enableothers of ordinary skill in the art to understand the embodimentsdisclosed herein.

What is claimed is:
 1. A quantum circuit, comprising: a nanowire on asubstrate, wherein the nanowire is configured to connect a quantum dotJosephson junction and a Dolan bridge Josephson junction in series; afirst lead and a second lead on top of the substrate, the first lead andthe second lead extending substantially perpendicular to the nanowireand providing the quantum dot Josephson junction; and a third lead and afourth lead on top of the substrate, the third lead extendingsubstantially perpendicular to the fourth lead and the nanowire, and thethird lead and the fourth lead providing the Dolan bridge Josephsonjunction.
 2. The quantum circuit according to claim 1, wherein thesubstrate comprises a first portion forming the nanowire and a secondportion surrounding the first portion.
 3. The quantum circuit accordingto claim 2, wherein the first portion of the substrate forming thenanowire comprises indium arsenide (InAs).
 4. The quantum circuitaccording to claim 2, wherein the second portion of the substratecomprises InAs implanted with ions.
 5. The quantum circuit according toclaim 4, wherein the ions comprise helium ions, oxygen ions, argon ions,or hydrogen ions.
 6. The quantum circuit according to claim 1, whereinthe nanowire has a width less than 50 nm, and a length between 100 nmand 1000 nm.
 7. The quantum circuit according to claim 1, wherein thesubstrate comprises gallium arsenide (GaAs).
 8. A method of producing aquantum circuit, comprising: forming a nanowire on a substrate, whereinthe nanowire is configured to connect a quantum dot Josephson junctionand a Dolan bridge Josephson junction in series; forming a first leadand a second lead on top of the substrate via liftoff processing, thefirst lead and the second lead extending substantially perpendicular tothe nanowire and providing the quantum dot Josephson junction, whereinthe liftoff processing comprises deposition of a first liftoff mask ontop of the substrate, deposition of a first metal on top of the firstliftoff mask, and lifting off the first liftoff mask; and forming athird lead and a fourth lead on top of the substrate via the liftoffprocessing, the third lead extending substantially perpendicular to thefourth lead and the nanowire, and the third lead and the fourth leadproviding the Dolan bridge Josephson junction, wherein the liftoffprocessing comprises deposition of a second liftoff mask on top of thesubstrate, deposition of a second metal on top of the second liftoffmask, and lifting off the second liftoff mask.
 9. The method accordingto claim 8, wherein forming the nanowire comprises covering a firstportion of the substrate with a photoresist wherein the photoresist hasa size substantially similar to a size of the nanowire to be formed. 10.The method according to claim 9, wherein forming the nanowire furthercomprises implanting a second portion of the substrate with ions,wherein the second portion of the substrate is not covered by thephotoresist.
 11. The method according to claim 10, wherein the ionscomprise helium ions, oxygen ions, argon ions, or hydrogen ions.
 12. Themethod according to claim 8, wherein the nanowire has a width less than50 nm, and a length between 100 nm and 1000 nm.
 13. The method accordingto claim 8, wherein the first metal and the second metal comprisealuminum, lead, titanium, tungsten or vanadium.
 14. The method accordingto claim 8, wherein the substrate comprises gallium arsenide (GaAs). 15.A quantum computer, comprising: a refrigeration system under vacuumcomprising a containment vessel; and a qubit chip contained within arefrigerated vacuum environment defined by the containment vessel,wherein the qubit chip comprises a quantum circuit; and anelectromagnetic waveguide arranged within the refrigerated vacuumenvironment so as to direct electromagnetic energy to and receiveelectromagnetic energy from the quantum circuit, wherein the quantumcircuit comprises: a nanowire on a substrate, wherein the nanowire isconfigured to connect a quantum dot Josephson junction and a Dolanbridge Josephson junction in series; a first lead and a second lead ontop of the substrate, the first lead and the second lead extendingsubstantially perpendicular to the nanowire and providing the quantumdot Josephson junction; and a third lead and a fourth lead on top of thesubstrate, the third lead extending substantially perpendicular to thefourth lead and the nanowire, and the third lead and the fourth leadproviding the Dolan bridge Josephson junction.
 16. The quantum circuitaccording to claim 15, wherein the substrate comprises a first portionforming the nanowire and a second portion surrounding the first portion.17. The quantum circuit according to claim 16, wherein the first portionof the substrate forming the nanowire comprises indium arsenide (InAs),and wherein the second portion of the substrate comprises InAs implantedwith ions.
 18. The quantum circuit according to claim 17, wherein theions comprise helium ions, oxygen ions, argon ions or hydrogen ions. 19.The quantum circuit according to claim 15, wherein the nanowire has awidth less than 50 nm, and a length between 100 nm and 1000 nm.
 20. Thequantum circuit according to claim 15, wherein the substrate comprisesgallium arsenide (GaAs).